Overview
The hyoid apparatus (apparatus hyoideus) is a set of articulated small bones that hangs from the tympanic region of the skull and supports the root of the tongue, the pharynx and the larynx. It lies between the rami of the mandible and does not articulate with it.
Components
- Tympanohyoid cartilage: attaches the chain to the mastoid region of the temporal bone.
- Stylohyoid, epihyoid and ceratohyoid: on each side they form the suspensory chain, running rostroventrally from the skull to the body of the hyoid.
- Basihyoid: unpaired transverse bone at the root of the tongue; it is the body of the apparatus.
- Thyrohyoids: run caudally from the basihyoid and articulate with the thyroid cartilage of the larynx.
In the domestic cat every element of the suspensory chain is ossified. In the big cats that roar (Panthera), by contrast, the epihyoid is replaced by an elastic ligament; this difference has classically been linked to the ability to roar or to purr, although purring is produced in the larynx by the rhythmic contraction of its intrinsic muscles.
Functions
- Support and movement of the tongue: many lingual muscles (hyoglossus, geniohyoideus) anchor on it.
- Positioning of the larynx during swallowing.
- Attachment of neck muscles such as the sternohyoideus and thyrohyoideus.
Clinical relevance
- Linear foreign bodies: thread and string often loop around the base of the tongue; look for them by lifting the tongue in every vomiting cat.
- Radiography: the hyoid bones are visible on lateral views of the head and neck and must not be mistaken for foreign bodies.
- Trauma: fractures are rare; they follow strangulation or blows to the neck and can cause dysphagia.
In this model the hyoid apparatus is illustrative geometry; its shape and position are approximate.